Pulsed light provided by sources such as flashlamps and lasers have been used for several years for the removal of unwanted hair, and for treatments such as removal of pigmentation or vascular lesions.
Pulsed light sources may act through a number of mechanisms, including photomechanical disruption, photothermal ablation, photochemical ablation and photothermal coagulation/denaturation. Some of these light sources act by purely non-thermal means (i.e. mode-locked or Q-switched short pulse lasers) and others use a thermal effect to produce ablation or disruption of tissue. The most widely used and successful light sources for depilation or removal of pigmented and vascular lesions employ a photothermal interaction in which the mechanism of action is pulsed light used to locally heat the lesion or hair follicle with one or more closely spaced pulses in order to raise the temperature of the targeted tissue during or immediately following a single pulse to a temperature which will cause the death, damage, or reduced function, or reduced viability of the targeted tissue. The higher absorption of the target tissue will elevate its temperature with respect to the surrounding tissue, resulting in selective thermal destruction of the lesion or follicle, while the surrounding tissue will not be raised to a temperature which causes thermal destruction. Prior devices relied on relatively high power pulses of light (electromagnetic radiation) from a light source, such as a laser or a flashlamp. For example, typical prior devices provide energy pulses in the range of 10-40 J/cm2 for a treatment provided to a selected area. Some of these prior devices provide for supplying a single pulse providing the treatment energy. Other prior devices utilize a series of closely spaced lower energy pulses, where the frequency of the pulses may be in the range of 10 hz or higher, which corresponds to a time between pulses of 100 ms or less. FIG. 1 shows part of a series of pulses which generally represents a pulse treatment which would be provided using a typical system and method of prior thermal treatment devices. As shown in FIG. 1 a period between pulses T is provided. Depending on the particular system this might range from 1 ms, or slightly less, to as much as 100 ms for treating hair follicles or treatment of skin pigmentation. The pulse width PW would typically be in the range of 2-5 ms. In applications for the treatment of skin pigmentation and removal of hair follicles, and for applications utilizing a flashlamp, the period between pulses was typically far less than 100 ms between pulses. In many other applications, for example, treatments for the removal of melanin-bearing sun damaged spots on skin, the treatment times may be as short as 5 ms, or even shorter.
One issue with present systems is that because a relatively large amount of fluence and power applied to the skin, an incorrect setting in terms of the fluence or time of treatment can cause unwanted results, and in some cases can result in scarring, hypopigmentation or hyperpigmentation. For example, consider a situation in which a fluence of 40 J/cm2 is delivered to a treatment area during a 10 ms pulse width, the peak intensity for this treatment would be 4,000 W/cm2. Because the treatment time is so short, there is a possibility that a patient would receive too much energy in too short of a time period which could result in a treatment area receiving an excess amount of energy and might cause unwanted damage to the tissue. Further, because the treatment energy is applied over such a short time period, the patient's natural pain reflex may not be fast enough to allow a patient to discontinue the treatment, prior to severe overheating of the tissue. Thus, these prior systems typically require trained and qualified medical personnel to apply the treatment. Such devices are therefore not safely or reasonably used directly by a patient or consumer.
Another issue with present systems is that they require relatively complex and expensive power supplies. This is because the appropriate energy must be delivered over a very short time, necessitating a highly rated high voltage power supply. In the past, the complexity of the power supply required that the power supply be housed in a module which was separated from the treatment device housing the flashlamp that provides light energy to the treatment area.
Additionally, because of the high treatment power used in prior systems, these systems must provide for a relatively sophisticated cooling system for keeping the temperature of critical system components sufficiently low, so that the energy being dissipated over a short time period will not cause the application device to become overheated.